airman vs first officer

airman

noun
  • A pilot of an aircraft. 

  • A naval seaman, especially one in the U.S. Navy, who works on and/or handles aircraft. 

  • A member of an air force. 

  • A person of a rank in the U.S. Air Force above airman basic and below airman first class. 

first officer

noun
  • The copilot of an aircraft. 

  • Air Transport Auxiliary rank corresponding to Flight Lieutenant in the Royal Air Force. 

  • Women's Royal Naval Service rank corresponding to Lieutenant-Commander in the Royal Navy. 

  • The chief mate of a merchant ship. 

  • The executive officer, second in command of a naval vessel. 

  • The most senior civil servant in the United States Foreign Service, with responsibility for running an embassy under the authority of and reporting to the ambassador. 

How often have the words airman and first officer occurred in a corpus of books? (source: Google Ngram Viewer )